Nanostructure "Sandwich" Triples Efficiency of Organic Solar Cells

Researchers at Princeton University have come up with a way to triple the efficiency of organic solar cells, the flexible plastic cells that are cheaper to manufacture than the brittle crystalline silicon cells conventionally used in solar panels and could be used in a variety of applications.

The research team came up with a nanostructure design that sandwiches a layer of plastic and metal together to more effectively trap light in the cell and boost the electricity that is generated. The researchers, led by electrical engineer Stephen Chou, were able to increase the efficiency of the solar cells 175 percent and they believe that the same technology could be applied to conventional silicon cells and have similar results.

The researchers say the the nano-sandwich is a subwavelength plasmonic cavity, which both decreases the amount of light reflected by a solar cell and traps more light to begin with. The new solar cell design was able to cut reflection down to only about 4 percent of light and boost absorption up to 96 percent. Those improvements resulted in a 52 percent increase in efficiency in direct sunlight and even bigger gains -- 81 percent -- during cloudy days or when the solar cell is not directly facing the sun, compared to organic solar cells without the nano-sandwich.

Princeton explains, "The solar cell's features — the spacing of the mesh, the thickness of the sandwich, the diameter of the holes — are all smaller than the wavelength of the light being collected. This is critical because light behaves in very unusual ways in subwavelength structures. Chou's team discovered that using these subwavelength structures allowed them to create a trap in which light enters, with almost no reflection, and does not leave."

Because the structure traps light regardless of the electricity-generating material in the middle layer, the technology could be used with conventional silicon solar cells and actually help to decrease the thickness of silicon used, which would make those solar panels more flexible and less expensive to manufacture.

The researchers say the technology, which they're calling "plasmonic cavity with subwavelength hole array" or PlaCSH, is ready for commercialization, but that there will likely be a transition period before it's widely adopted. The good thing is that the nanostructure can be easily produced in wallpaper-size sheets using a technique called nanoimprint, a low-cost nanofabrication technique Chou invented 16 years ago, which embosses nanostructures over a large area, like printing a newspaper.